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Message-ID: <20190129164208.GF29981@quack2.suse.cz>
Date: Tue, 29 Jan 2019 17:42:08 +0100
From: Jan Kara <jack@...e.cz>
To: yangerkun <yangerkun@...wei.com>
Cc: jack@...e.cz, miaoxie@...wei.com, yi.zhang@...wei.com,
houtao1@...wei.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/2] ext2: get the exact max filesize in ext2_max_size
On Wed 23-01-19 21:14:09, yangerkun wrote:
> When mkfs.ext2 with '-b 65536' and mount(arm 64KB page size), function
> mount_fs will trigger WARNING since ext2_max_size will return value less
> than 0. Also, we cannot write any file in this fs since the sb->maxbytes
> is less than 0.
>
> Fix it by get the exact max file size. First, get the max depth for
> indirect blocks and check does the max data blocks add indirect blocks
> will execced upper_limit. If right, bisect to get exact data blocks
> number which satisfy 'data blocks number + indirect blocks number ==
> upper_limit'.
>
> Signed-off-by: yangerkun <yangerkun@...wei.com>
Thanks for the patches but I was really looking for something simpler.
Something like the attached patch. Although your more precise function will
raise the maximum file size by couple of kilobytes I don't think the
complexity is really worth it...
Honza
> ---
> fs/ext2/super.c | 115 ++++++++++++++++++++++++++++++++++++++++++++------------
> 1 file changed, 92 insertions(+), 23 deletions(-)
>
> diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> index 73b2d52..b3eb6e9 100644
> --- a/fs/ext2/super.c
> +++ b/fs/ext2/super.c
> @@ -753,11 +753,16 @@ static int ext2_check_descriptors(struct super_block *sb)
> * block limit, and also a limit of (2^32 - 1) 512-byte sectors in i_blocks.
> * We need to be 1 filesystem block less than the 2^32 sector limit.
> */
> -static loff_t ext2_max_size(int bits)
> +static loff_t ext2_max_size(struct super_block *sb, int bits)
> {
> - loff_t res = EXT2_NDIR_BLOCKS;
> - int meta_blocks;
> + loff_t res;
> + loff_t max_meta_blocks;
> + loff_t used_data_blocks;
> + loff_t max_data_blocks;
> loff_t upper_limit;
> + int depth;
> + loff_t high, low;
> +
>
> /* This is calculated to be the largest file size for a
> * dense, file such that the total number of
> @@ -771,24 +776,88 @@ static loff_t ext2_max_size(int bits)
> /* total blocks in file system block size */
> upper_limit >>= (bits - 9);
>
> + /* Try to get max depth of metadata blocks */
> + depth = 0;
> + max_meta_blocks = 0;
> + used_data_blocks = 0;
> + max_data_blocks = EXT2_NDIR_BLOCKS;
> + if (max_meta_blocks + max_data_blocks > upper_limit)
> + goto bisect;
> +
> + depth++;
> + max_meta_blocks = 1;
> + used_data_blocks = max_data_blocks;
> + max_data_blocks += 1LL << (bits - 2);
> + if (max_meta_blocks + max_data_blocks > upper_limit)
> + goto bisect;
> +
> + depth++;
> + max_meta_blocks += 1 + (1LL << (bits - 2));
> + used_data_blocks = max_data_blocks;
> + max_data_blocks += 1LL << (2 * (bits - 2));
> + if (max_meta_blocks + max_data_blocks > upper_limit)
> + goto bisect;
> +
> + depth++;
> + max_meta_blocks += 1 + (1LL << (bits - 2)) + (1LL << (2 * (bits - 2)));
> + used_data_blocks = max_data_blocks;
> + max_data_blocks += 1LL << (3 * (bits - 2));
> + if (max_meta_blocks + max_data_blocks > upper_limit)
> + goto bisect;
> +
> + goto out;
> +bisect:
> + low = 0;
> + if (depth == 0)
> + high = EXT2_NDIR_BLOCKS;
> + else
> + high = 1 << (depth * (bits - 2));
> + while (low <= high) {
> + int offsets[4];
> + loff_t mid = (low + high) >> 1;
> + depth = ext2_block_to_path(sb, mid + used_data_blocks - 1, offsets, NULL);
> + if (!depth)
> + return -EIO;
> +
> + max_meta_blocks = 0;
> + if (depth == 1)
> + max_meta_blocks = 0;
> +
> + if (depth == 2)
> + max_meta_blocks = 1;
> +
> + if (depth == 3) {
> + /* Indirect blocks */
> + max_meta_blocks += 1;
> + /* Double indirect blocks */
> + max_meta_blocks += 1;
> + max_meta_blocks += offsets[1];
> + }
>
> - /* indirect blocks */
> - meta_blocks = 1;
> - /* double indirect blocks */
> - meta_blocks += 1 + (1LL << (bits-2));
> - /* tripple indirect blocks */
> - meta_blocks += 1 + (1LL << (bits-2)) + (1LL << (2*(bits-2)));
> -
> - upper_limit -= meta_blocks;
> - upper_limit <<= bits;
> -
> - res += 1LL << (bits-2);
> - res += 1LL << (2*(bits-2));
> - res += 1LL << (3*(bits-2));
> - res <<= bits;
> - if (res > upper_limit)
> - res = upper_limit;
> -
> + if (depth == 4) {
> + /* Indirect blocks */
> + max_meta_blocks += 1;
> + /* Double indirect blocks */
> + max_meta_blocks += 1 + (1 << (bits - 2));
> + /* Tripple indirect blocks */
> + max_meta_blocks += 1;
> + if (offsets[1])
> + max_meta_blocks += (offsets[1] - 1) * (1 << (bits - 2));
> +
> + max_meta_blocks += 1;
> + max_meta_blocks += offsets[2];
> + }
> + if (max_meta_blocks + mid + used_data_blocks > upper_limit)
> + high = mid - 1;
> + if (max_meta_blocks + mid + used_data_blocks < upper_limit)
> + low = mid + 1;
> + if (max_meta_blocks + mid + used_data_blocks == upper_limit) {
> + max_data_blocks = mid + used_data_blocks;
> + break;
> + }
> + }
> +out:
> + res = max_data_blocks << bits;
> if (res > MAX_LFS_FILESIZE)
> res = MAX_LFS_FILESIZE;
>
> @@ -995,7 +1064,9 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
> }
> }
>
> - sb->s_maxbytes = ext2_max_size(sb->s_blocksize_bits);
> + sbi->s_addr_per_block_bits =
> + ilog2 (EXT2_ADDR_PER_BLOCK(sb));
> + sb->s_maxbytes = ext2_max_size(sb, sb->s_blocksize_bits);
> sb->s_max_links = EXT2_LINK_MAX;
>
> if (le32_to_cpu(es->s_rev_level) == EXT2_GOOD_OLD_REV) {
> @@ -1035,8 +1106,6 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
> sizeof (struct ext2_group_desc);
> sbi->s_sbh = bh;
> sbi->s_mount_state = le16_to_cpu(es->s_state);
> - sbi->s_addr_per_block_bits =
> - ilog2 (EXT2_ADDR_PER_BLOCK(sb));
> sbi->s_desc_per_block_bits =
> ilog2 (EXT2_DESC_PER_BLOCK(sb));
>
> --
> 2.9.5
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
View attachment "0001-ext2-Fix-underflow-in-ext2_max_size.patch" of type "text/x-patch" (2642 bytes)
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